Field of the Invention
Embodiments of the present invention generally relate to an expandable liner. In particular, embodiments of the present invention relate to an expandable liner for a fracturing operation and methods of installing the liner.
Description of the Related Art
Expandable tubular liners have been used in existing wellbores as a repair liner or in open hole as a drilling liner. These liners can be just a few joints of pipe or can be more than one hundred joints. These joints may be 30 to 40 feet in length and are connected using a threaded connection. In some instances, the connection is a flush pipe connection, which has a similar wall thickness to the pipe wall thickness. This type of connection will be much weaker in tension, compression, or bending than the pipe body. For example, these expandable threaded connections may have tension and compression strengths that are about 50% of the pipe body.
In most repair or open hole applications, the tension or compression loads applied to the unexpanded connections is equal to the buoyed weight of the liner, plus any bending that might be present. In the case of the liner being set at bottom of the well, the liner would experience a compression load due to its own weight. After expansion, the liner may be fixed against the outer or parent casing or open hole by the expanded external rubber seals. In this position, applied internal or external pressure may cause the liner to shrink. However, because the liner is fixed and cannot shrink, the liner and its connections will experience additional tension loads as a consequence of the applied pressure.
Changes in wellbore conditions may increase the tension load on the expandable tubular connection. In addition to the tension load generated during expansion, there are at least three other potential sources of tension load. The tension loads from these sources are additive. If they occur, the total tension load can be enough to cause a connection to fracture. Even without connections, the tension can be enough to cause the pipe body itself to fail.
The first source of tension load is trapped expansion force due to the expanded liner being fixed to the outer casing by the compressed rubber seals in the annulus between the liner and the casing. Although these seals are desirable for blocking annulus communication, they are also the problem with the tension load build up. During expansion, the expansion force is locked into the liner and connections between the rubbers because the liner is expanded using a tension constraint. That is, as the expansion cone is being pulled through the liner while the bottom of the liner is fixed to the parent casing, all of the liner between the anchor and the cone is in tension. As the cone passes through each rubber seal, that tension in the liner is trapped and permanent.
A second source for load build up is thermal changes in the wellbore. For example, a wellbore fluid is initially at ambient temperature when it is at the surface. When it goes downhole, it cools the liner which is at the production zone temperature or bottom hole temperature, which may be at 300° F. As the liner is cooled by the wellbore fluid, the liner will tend to shrink in length. However, because the liner is trapped in place by the rubber seals and therefore, cannot shrink in length, the liner will experience a tension load build up that will remain until the temperature goes back up. Conversely, if the temperature is increased (e.g., steam injection), the liner would tend to grow in length. Because it cannot do so as a result of being fixed by the seals, the load experienced by the liner will be a compression load.
A third source for load build up is pressure changes inside the expanded liner. High pressure fluid inside the expanded liner may cause the liner to want to grow circumferentially, which would normally cause a liner to shrink in length. This is often called the Poisson Effect. Again, because the seals or anchors do not allow the liner to shrink in length, a tension load is generated.
Finally, if the liner is blocked off by a plug or ball situated at the bottom of the liner or other sections of the liner, high pressure in the liner may create a downward force (or end thrust) on the plug, thereby generating a tension load in the liner between the plug and the expanded seal that is located above and closest to the plug.
Because these loads are additive, the result is the potential to build up load beyond the connection's ability to resist the load. The total tension load can build up to more than three times the elastic limit or two times the ultimate strength (or point of fracture). These additional tension loads are constant along the length of the liner. Therefore, under these loads, a connection would break in between every pair of external rubber seals.
There is, therefore, a need for an expandable liner capable of handling changes in tension loads. There is also a need for a method of installing an expandable liner to withstand changes in tension loads caused by high pressures.